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The thymus is a central lymphoid organ primarily responsible for the development of T cells. A small proportion of B cells, however, also reside in the thymus to assist negative selection of self-reactive T cells. Here we show that the thymus of human neonates contains a consistent contingent of CD138+ plasma cells, producing all classes and subclasses of immunoglobulins with the exception of IgD. These antibody-secreting cells are part of a larger subset of B cells that share the expression of signature genes defining mouse B1 cells, yet lack the expression of complement receptors CD21 and CD35. Data from single-cell transcriptomic, clonal correspondence and in vitro differentiation assays support the notion of intrathymic CD138+ plasma cell differentiation, alongside other B cell subsets with distinctive molecular phenotypes. Lastly, neonatal thymic plasma cells also include clones reactive to commensal and pathogenic bacteria that commonly infect children born with antibody deficiency. Thus, our findings point to the thymus as a source of innate humoral immunity in human neonates. The thymus is known as the organ of T lymphocyte development. Here authors show that terminal B cell differentiation also takes place in the thymus of human neonates, leading to antibody production against commensal and pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Background. The relationship between circulating effector memory T and B cells long after transplantation and their susceptibility to immunosuppression are unknown. To investigate the impact of antirejection therapy on T cell-B cell coordinated immune responses, we assessed IFN-γ-producing memory cells and natural antibodies (nAbs) that potentially bind to autoantigens on the graft. Methods. Plasma levels of IgG nAbs to malondialdehyde (MDA) were measured in 145 kidney transplant recipients at 5–7 years after transplantation. In 54 of these patients, the number of donor-reactive IFN-γ-producing cells was determined. 35/145 patients experienced rejection, 18 of which occurred within 1 year after transplantation. Results. The number of donor-reactive IFN-γ-producing cells and the levels of nAbs were comparable between rejectors and nonrejectors. The nAbs levels were positively correlated with the number of donor-reactive IFN-γ-producing cells (rs = 0.39, p = 0.004). The positive correlation was only observed in rejectors (rs = 0.53, p = 0.003 ; nonrejectors: rs = 0.24, p = 0.23). Moreover, we observed that intravenous immune globulin treatment affected the level of nAbs and this effect was found in patients who experienced a late ca-ABMR compared to nonrejectors (p = 0.008). Conclusion. The positive correlation found between alloreactive T cells and nAbs in rejectors suggests an intricate role for both components of the immune response in the rejection process. Treatment with intravenous immune globulin impacted nAbs. [ABSTRACT FROM AUTHOR]

Antibody mediated rejection (AMR) is an increasingly studied cause of graft failure after heart transplantation. AMR diagnosis previously required the detection of circulating donor specific antibodies (DSA); however, the most recent criteria only require pathological findings. This classification defined a subset of patients with AMR, yet without known antibodies. Here, we sought to evaluate differences in the transcriptome profile associated with different types of AMR. RNA sequencing was used on endomyocardial biopsies to analyze and compare transcriptomic profiles associated with different subtypes of AMR defined by immunopathological and histopathological findings, as well as the presence or absence of DSA. Gene expression profiles were characterized for each diagnostic group. The most divergent gene expression profiles were observed between patients with or without DSA. AMR subtypes associated with DSA showed expression of signature genes involved in monocyte activation and response to interferon. There was also substantial difference between the transcriptomic profiles of AMR defined by histopathological and immunopathological findings, the latter being associated with expression of mucin genes. In contrast, there was no differential RNA expression between patients with pAMR1i without DSA and those without AMR. Likewise, no differential expression was observed between patients with pAMR1h with DSA and pAMR2. Overall, our studies reveal different expression profiles in endomyocardial biopsies in relation to some key criteria used to diagnose AMR. These findings support the view that the diagnosis of AMR encompasses several phenotypes that may rely on distinct mechanisms of injury. [ABSTRACT FROM AUTHOR]

It is well established that HLA antibodies play an important role in antibody-mediated rejection (AMR) and there is a growing body of literature demonstrating that non-HLA antibodies may also contribute to AMR. To study the source of non-donor specific HLA antibodies and self-reactive antibodies in patients with kidney graft loss, Porcheray et al. (Am J Transplant 2012; 12: 2088–2097) expanded immortalized polyreactive B-cell clones from a patient with kidney graft rejection and showed that some of these natural antibodies are cross-reactive to HLA and self-antigens. Gao et al. (Am J Transplant 2014; 14:1581–1591) also showed that the presence of IgG natural antibodies, with activity to apoptotic cells, correlates with late kidney allograft loss even after excluding patients with high reactivity to HLA. We have further characterized the HLA reactivity of 4 polyreactive B-cell clones isolated by Porcheray, Gao et al. using solid phase assays (Immucor, Inc.). We report here that while these clones do not react with HLA on the Immucor single antigen beads, they react to other HLA products, with some variation between different solid phase assays. Their reactivity appears to be enhanced upon denaturation, as judged by the monoclonal antibody 210.4, which reacts with denatured antigen, suggesting that they primarily react to cryptic epitopes. B. Ray: Employee; Company/Organization; Immucor. [ABSTRACT FROM AUTHOR]